The invention relates generally to a feed shoe of the type used in powder metallurgy processes, for feeding and depositing finely divided or pulverized particulate material, such as powdered metals and the like, into a die cavity for compacting. More particularly, the invention relates to a feed shoe having an adjustable gate member incorporated into a front portion of the feed shoe.
In powder metallurgy and other technologies using particulate materials, such as ceramics and carbides, products and parts are formed by pressing finely ground or atomized powders into a desired shape within a die cavity. Generally, the powders are compacted in the die cavity at room temperature and the then semi-dense compact is removed from the die and heated to bond the powders into a unified, dense mass. In powder metallurgy, the heat bonding procedure is generally known as sintering or in the case of ceramics and carbides, firing.
When these and similar procedures are employed, means are required for delivering measured amounts of powder or particulate to a die cavity on a powder press. Typically, feed shoes operate to deliver the powder or particulate material to the die cavity during the press cycle, commonly using a gravity assisted fill system, although pressure and vacuum assisted systems are also known. The process involves movement of the feed shoe containing particulate material on a shuttle which slides the feed shoe forward along the table of the die press to a position at which the bottom hole in the feed shoe is exposed, overlies, and registers with the die cavity, and deposits enough loose powder to fill the die cavity. Thereafter, the shuttle slides the feed shoe back along the table of the die press into a retracted position, which cuts off the flow of particulate material from the bottom hole of the feed shoe into the die cavity. The edge of the bottom hole of the feed shoe also levels off excess powder from the top of the filled die cavity as the feed shoe is retracted. The particulate material is then pressed into an article and the article is ejected from the die. The shuttle then slides the feed shoe forward along the table of the die press displacing the ejected article and again exposing the bottom hole of the feed shoe as it overlies and registers with the die cavity, and the process is repeated.
The design of the feed shoe is critical to the quality of the part being produced. However, conventional feed shoes typically are of a general design, configured to give average results when used to produce parts of an average geometry and size. In some application, for example the production of thermal battery pellets, the pellets can be disproportionately thin compared to the overall size, making the pellets naturally difficult to produce. One of the most notable problems is the die fill consistency. The thickness of the pellets makes it difficult to get an even die fill from front to back, thus magnifying the powder fill imbalance that is already an inherent problem with conventional die fill methods. “Powder pull-out,” which is the tendency of the leading edge of the bottom hole in the feed shoe to drag feed material from the front to the back of the die cavity, typically occurs in the front of the die cavity as the feed shoe is retracted after filling the die cavity. In addition, the conventional feed shoe design does not allow thickness adjustment on a part from side to side which occurs as a result of tooling flatness, press set up, and the like. These are major problems for parts that are very thin to begin with, leading to tapered thickness, poor strength, and an increased number of rejected parts.
The conventional feed shoes can also perform inadequately in regard to providing weight consistency between die cavities in dual die cavity platforms, thus limiting the capability to press pellets with large areas and obtain the increased production benefits of dual cavity pressing. Also, the feed tube which delivers feed material, e.g., powder, into the feed chamber is not necessarily configured for optimum, even powder distribution across the width of the feed chamber. This likewise leads to inconsistent die cavity fill; in this case, from side to side. Moreover, the conventional feed shoe design is not conducive to low press cycle times. In particular, the configuration of the conventional feed shoe requires the top ram has to have a relatively high vertical travel in order to clear the feed shoe during the die cavity fill operation, thus increasing the overall cycle time.
Accordingly, there is a need for an improved feed shoe which is configured to reduce or eliminate the problems which can be common with conventional feed shoes described hereinabove.